Unfortunately, they cancelled the opportunity because they didn't get very many submissions, so I can't present it at the conference. This means I have to find another way to get feedback and/or show it to the public. So here I am posting in the non-hiking section that almost nobody reads, kind of at a loss of what to do after putting a bit of time and effort into developing this idea. Curious...what do you think of the idea? Who should I contact to share this with? Is there anybody interested in running a simulation on a computer or building a prototype and testing?

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So, basically, air is drawn in remotely, passes underground where it cools by virtue of contact with the surrounding earth (or water), and by the time it reaches the AC unit, a good deal of cooling has already transpired, therefore requiring less energy.

How much will the ground 20' down warm up due to passing 115 degree air through it? Won't the walls of the conduit become fairly warm thus reducing the cooling effect? A pool might be better since water will radiate away the heat more effectively, but a pool will become warm in the sun since typically a pool will be open to the sun at the surface.

You could have water circulating around the underground air intake, but that takes a lot more construction effort.

Perhaps it would help even more to bury or at least partially recess the house. Additionally, the construction of a shade of some sort such that the house is not directly hit by the sun would be a great help in keeping things cool.

Yeah, that's the general idea. Even if the AC unit is set to recirculate, it still saves electricity because cooler air is flowing through the condenser coil. The walls of the conduit and surrounding ground would heat up, but I think that cooling ability depends greatly on how it's engineered. To get the most out of the ground without doing anything too elaborate, several pipes running in parallel would create more heat transfer. The pipe walls cool again at night time, and the surrounding ground cools again in winter if you run the AC system in reverse as a heat pump, especially at night.

Perry, I have seen this idea put into practice. It was a very large custom home built in Riverside. The depth was not nearly as deep as you propose, but instead was only about 3 feet under the slab. In order to have the desired effect, it ran the entire length of the house. I believe the owner told me that it was common practice where he grew up. I don't know how well it worked, but it did work.

HJ, I did some thinking... Originally I wanted to keep this as simple and fail-proof as possible. However, I will probably hear more criticism about heat transfer issues than about the cost and reliability of a custom water tank. My opinion at this point is that it's possible with parallel pipes and no water tank, but I agree that the water would improve performance, and I'm going to create a new image with parallel pipes inside separate water tanks (in case one leaks) and also draw an AC unit that can run in reverse in winter.

I think a window AC unit would work with pipes in the south (shaded) end of a pool. Does anybody know typical temperatures for an unheated pool in the desert during summer time? This method would also heat the pool.

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There's a lot of good stuff there. That's great to see that the government of Australia is so interested in conservation methods. The "whole of house fans" method could be used at night time in fall and spring here in the desert. That page is dedicated to passive cooling methods, with fans considered to be passive. I didn't see AC airflow heat exchange with the ground or pond on that page.

That's not to say that your friend isn't doing it. It wouldn't surprise me if somebody, somewhere, is already doing this idea. Would your friend be interested in posting here or talking about it?

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This drawing is not to scale. I got frustrated with Inkscape because it has programming bugs. The parallel pipes would need to be small diameter to transfer heat, and the black box would need a lot of surface area, possibly running the full length of the house to create enough buoyancy to compensate for the air resistance (pressure drop) of the small pipes.

If the water tanks are very deep and the A/C system runs in reverse in winter, it may work better on the south side of the building because it's easier to make a large black chimney, and the majority of heat transfer to and from deep underground would be from airflow through the small pipes, not thermal conductivity from the surface. After a couple years of use, it would reach approximately 75 F regardless of surface conditions.

I clicked around on the Australian site some more. There's a brief mention:

Air-to-water or air-to-ground (also called geothermal) exchangers are far more efficient. Heat exchange pipes are run through a body of water or deep into the ground where the temperature is relatively stable all year round.